The invention concerns a method in a paper machine, coating machine, intermediate winder, unwind stand of a slitter-winder, or in any other device for treatment of a web.
A particular subject of the invention is a method in splicing in a continuous unwind stand, in which method the web on a new machine reel to be introduced in the unwind stand is joined at full speed with the web of the machine reel that is being emptied by cutting off the web and by pressing the web of the machine reel that is being emptied into contact with the splice provided on the new machine reel.
A second particular subject of the invention is a method in equipments for coating of a paper web, in which method the paper web is coated with a layer of paste from at least one side by making the paper web pass through at least one coating station and through at least one dryer section, and in which method the running of the paper web to be coated is monitored by means of at least one monitoring device, the cutting off of the paper web to be coated being carried out based on a signal transmitted by said monitoring device.
The invention also concerns a device in a paper machine, coating machine, intermediate winder, unwind stand of a slitter-winder, or in any other device for treatment of a web.
A particular subject of the invention is also a device in splicing in a continuous unwind stand, in which the web on a new machine reel to be introduced in the unwind stand is joined at full speed with the web of the machine reel that is being emptied by cutting off the web and by pressing the web of the machine reel that is being emptied into contact with the splice provided on the new machine reel.
A second particular subject of the invention is also a device in equipments for coating of a paper web, by means of which coating machine the paper web is coated with a layer of paste from at least one side by making the paper web pass through at least one coating station and through at least one dryer section, and in which coating machine the running of the paper web to be coated is monitored by means of at least one monitoring device.
In off-machine coating machines, a continuous unwind stand is used in which the new machine reel to be introduced in the unwind stand is joined at full speed with the tail of the machine reel that is being emptied. In modem high-speed coating machines, the splicing method is, in principle, the same irrespective of the manufacturer of the machine. At the end of the web on the new machine reel, in advance, a splice is prepared by means of double-sided adhesive tape, which splice is attached to the reel face by means of pieces of adhesive tape. The circumferential speed of the new machine reel is raised to a level equal to the running speed of the machine, after which the web of the machine reel that is being emptied is pressed into contact with said splice, for example, by means of a roll or brush. The old web is cut off by means of a blade from above the splice.
The splicing in an unwind stand has become problematic at the current running speeds (1200 . . . 1600 meters per minute). Out of this reason, the running speed of the splicing machine is often lowered for the time of splicing. At a high speed, a vacuum is formed in the what is called splicing gap placed between the machine reel and the splicing roll brought to the vicinity of said reel, which vacuum can be pulsating if the new machine reel is non-circular. The vacuum tends to attract the old web partly into contact with the splice even before splicing, and the vacuum also causes fluttering of the old web. Further, the vacuum tends to separate the tape splice from the face of the new machine reel, in which case the new machine reel is opened before splicing. In order that the running of the web should be controlled, at the splicing roll a bend is required, which again requires stretching of the web when the splicing roll is hit quickly onto the face of the new machine reel. Attempts are made to keep the tension peak caused by the hitting of the roll in splicing low by using a little splicing gap (8 . . . 12 mm), which produces an intensive vacuum effect. Even the bending angle that is used currently causes a problematic tension peak in the web. At higher running speeds an even larger bending angle would be required.
In the FI Patent Application No. 942869, a splicing device for a continuous unwind stand is described, by whose means the new machine reel brought to the unwind stand is connected at full speed with the web of the machine reel that is being emptied. The splicing device comprises a splicing roll, by whose means the web of the machine reel that is being emptied is pressed into contact with the splice placed on the new machine reel, and at least one second roll. The splicing roll and said second roll are attached to a lever device, which is mounted by means of an articulation point placed between the shafts of said rolls, so that the run of the web before splicing and the run of the web during splicing are such that the length of the web during splicing and when said rolls are in their basic positions is substantially equal.
At high running speeds and in particular with heavy paper grades, in flying splicing, a problem has been the control of the cut-off tail of the old machine reel. After the splicing, attempts are made to stop the reel spool that is being emptied quickly. Paper must not be unwound to such an extent that it cannot be controlled by means of blowing of air. The tail of the cut-off web and any paper chips must be kept away from the splicing nip. If the cut-off tail ends up onto the web, it causes a web break. Also smaller paper chips can cause a web break if chips are carried along with the web, for example, to a coating station. Even if a paper chip separated from the tail did not cause a web break, it, however, causes cleaning work after splicing.
In order to solve this problem, some manufacturers have constructed inverted unwind stands, in which the geometry has been turned upside down. It is the purpose of the inverted geometry that, after the splicing, the cut-off tail and any paper chips that are separated fall away from the web by the effect of gravity. At higher speeds (higher than 1400 meters per minute), even this is not of any use, because the air flows present on the faces of the departing web and of the large machine reel that is being unwound are so intensive that the direction of the gravity remains insignificant.
Traditionally, for the control of the cut-off web, blowings have been employed, by whose means attempts are made to guide the tail around the reel spool to be slowed down and to prevent access of the tail and of separated chips to the departing web. Attempts are made to stop the reel spool that is being emptied by means of mechanical brakes quickly. This requires high capacity from the brakes and, thereby, causes rapid wear of the brakes. The brake pads of the brakes must be renewed frequently. At present, a typical stopping time of about 4 seconds is in use. With the present-day technology, a target time for stopping the reel would be about 1.5 seconds, irrespective of the speed or of the size of the reel spool. In large machines, such a time would involve a braking capacity of up to 10 MW. At present, there are production machines in which the brake devices must be replaced even at intervals of 2 months, which means, among other things, a considerable expense in terms of money.
In very narrow unwind stands (width about 1 meter) of the revolver type, which are used at printing machines, occasionally, a double-sided tape is used on an intermediate roll placed before the cut-off roll, which tape captures the cut-off tail around it. After splicing, the intermediate roll is unwound and cleaned manually. The tape is difficult to remove from the intermediate roll, but this is necessary after each splicing cycle. In large high-speed unwind stands (roll diameter xcfx86=1000 mm, length 8000 mm) such fitting of tapes and manual cleaning are directly impossible, because there is not time enough for the necessary manual cleaning between splicing cycles.
In machines for coating of a paper web, first a layer of paste is applied onto the paper web by means of an applicator device, and after that the coating is smoothed by means of a doctor blade against the same backup roll.
In the Finnish Patent No. 93,665, a method and an equipment are described for coating of a paper web, wherein the application and the smoothing proper are arranged so that each process has a backup face of its own. Of the backup faces, at least the latter one drives the web or moves at least substantially at the same speed as the web. By means of independent backup faces, it is possible to control the tension of the web placed between the holding points and to prevent detrimental bag formation in, or slackening of, the web between the holding points.
In the Finnish Patent No. 94,883, a method and an equipment are described for double-sided coating of a thin printing-paper web that contains mechanical pulp. In this prior-art method, the first side of the web is coated by means of a first coating station, the first coating layer is dried at least partly by means of a drying equipment, and the second side of the web is coated, after drying of the first side, by means of a second coating station, and the second coating layer is dried at least partly by means of a second drying equipment. The first and the second coating layer are formed by applying the necessary amount of coating agent onto the face of a film roll, from which the coating agent is transferred onto the web in a nip between a backup roll and the film roll. The drying equipment can consist of infrared dryer units and of drying cylinders.
As is well known, in paper web coating machines, air dryers, i.e. airborne web dryers, have also been employed.
Clearing up of web breaks taking place in a coating machine requires an abundance of time from the operating team, and losses in production arise. The clearing up of a web break mainly consists of the following steps of work:
Clearing of paper chips from the machine, in particular from between the airborne web dryers.
Washing of the coating stations.
In order that winding of the web around the backup rolls could be avoided, which winding might damage the rubber-coated backup rolls, the coating machine is typically provided with a web break monitoring system and with cutter blades before each coating station. When it operates correctly, this system protects the backup rolls but may, otherwise, cause even more paper chips to be cleared from the machine than without web break monitoring. This comes from the fact that the web tension goes down to zero after the cutter blade has cut off the web, in which connection the free tail moves readily to the sides, is cut off when it strikes against the frames, and remains in its place, e.g., inside the airborne web dryers. Corresponding situations in which the control of the web is lost, in the event of a web break or when the web is cut off intentionally, also occur, among other things, in intermediate winders, slitter-winders, and even in paper machines in some cases.
The general object of the present invention is to provide an improvement of the prior-art methods and devices in a paper machine, coating machine, intermediate winder, unwind stand in a slitter-winder, or in any other device for treatment of a web in which detrimental disturbance may occur.
It is a particular object of the present invention to provide an improvement of the prior-art methods and devices in splicing in a continuous unwind stand.
It is a more specific object of the invention to provide a method and a device in splicing in a continuous unwind stand, in which the numerous adverse factors occurring in the prior-art solutions have been avoided.
It is a second particular object of the present invention to provide an improvement over the prior-art methods and devices in paper web coating machines.
It is a more specific object of the present invention to provide a method and a device which permit a substantial reduction of the quantity of broke from web break.
The method in accordance with the invention is characterized in that, in the event of disturbance, the web is made to be wound in a controlled way around at least one web guide roll.
A method in accordance with the invention is characterized in that the cut-off final end of the web on the machine reel that is being emptied is made to adhere to an intermediate roll placed before the cutter blade by means of suction while said intermediate roll revolves at the unwind speed.
A second method in accordance with the invention is characterized in that, controlled by the signal transmitted by the monitoring device, the cut-off web is made to be wound in a controlled way around a pick-up roll placed in the coating equipment.
The device in accordance with the invention is characterized in that the device comprises at least one web guide roll around which the web is made to be wound in a controlled way in the event of disturbance.
A device in accordance with the invention is characterized in that the device comprises an intermediate roll placed before the cutter blade, which intermediate roll comprises means for producing winding of the cut-off final end of the web onto said intermediate roll while said intermediate roll revolves at the unwind speed.
By means of the present invention, among other things, the necessity, characteristic of the prior-art solutions, to stop the old reel spool quickly is avoided, in which case the wear of the brake devices is less intensive, and equally large or efficient brake devices are not needed.
A device in accordance with the invention in connection with a coating equipment is characterized in that the device includes a pick-up roll, which comprises means for making the cut-off web to be wound around said pick-up roll.
In accordance with preferred embodiments of the invention, the pick-up roll is placed, in an off-machine coating machine, before the coating station and/or after air dryers.
In the commonest embodiment of the invention, in a paper machine, coating machine, intermediate winder, unwind stand of a slitter-winder, or in any other device for treatment of a web, at least one web guide roll is employed, around which the web is made to be wound in a controlled way in the event of disturbance. The web guide roll is preferably a suction roll. In connection with the web guide roll, if necessary, for example, an air foil box can be fitted. In the vicinity of the web guide roll, it is favourable to fit a plate-like member, which extends substantially across the entire width of the web guide roll in the cross direction. The plate-like member preferably comprises a first plate portion, which extends in the running direction of the arriving web at a distance from the path of running of the web. The plate-like member preferably also comprises a second plate portion, which extends along the face of the web guide roll at a distance from the web guide roll. The plate-like member can be provided with holes in order to permit flow of air through the plate-like member.
According to a preferred embodiment of the invention, before the cutter blade, an intermediate roll has been fitted, which comprises members for making the cut-off final end of the web to adhere to the intermediate roll while the intermediate roll revolves at the unwind speed. In a preferred embodiment of the invention, the intermediate roll is a suction roll, into which a vacuum is passed in connection with the splicing. The suction in the suction roll can be activated substantially at the time of reel change only, or, as an alternative, a constant slight vacuum is maintained in the suction roll in order to stabilize the run of the web, and substantially at the time of reel change the suction roll is subjected to an intensive suction.
An embodiment with a suction roll can be accomplished most advantageously so that an invariable vacuum is set for the suction roll, which vacuum is sufficient to suck the tail around the roll in a situation of reel change, but which vacuum does, however, not cut off the web or have an interfering effect on the run of the web during normal running.
In a second preferred embodiment of the invention, a fluid that increases the adhesion is applied to the intermediate roll placed before the cutter blade. Such a moistening jet affixes the cut-off final end of the web reliably to the intermediate roll. The reel spool of the machine reel that is being emptied is braked down by means of a brake generator and/or by means of a mechanical brake under control, so that the cut-off final end of the web can be wound back onto the reel spool of the emptied machine reel, for example, by means of a secondary winding drive. A mechanical brake is used in small unwind stands only. A brake generator is the most advantageous solution, in which connection the centre drive operates as the brake.
According to a further preferred embodiment of the invention, in connection with the intermediate roll placed before the cutter blade, an air foil box has been fitted, by whose means, after cutting off of the web, the final end of the cut-off web is made to be wound around the intermediate roll. The cut-off final end is guided by means of an air foil box fitted in connection with the intermediate roll and by means of air blowings arranged in said box, so that the web end is wound onto the intermediate roll placed before the cutter blade while said intermediate roll revolves at the unwind speed.
In the vicinity of the face of the intermediate roll, air jets favourably parallel to the sense of rotation of the roll as well as a carrier face have been fitted, which carrier face extends a certain distance around the roll, preferably almost from the web cut-off point to the vicinity of the nip between the roll and the web. Favourably, by means of an air jet provided in the air foil box next to the cutter blade, the cut-off tail is guided by means of a coanda effect into the space formed by the air foil box and the intermediate roll and further to around the intermediate roll.
In the present invention, it has been realized to make use of the signal given by the web break monitoring system so that, based on the signal given by the monitoring device, besides cutting-off of the web, a control impulse is also given to some actuator, such as, for example, actuators fitted on a roll or rolls, by means of which actuator the cut-off web can be wound in a controlled way around the roll. In the solution in accordance with the invention, the web break is detected favourably so that (a pair of) photocells detects that the web xe2x80x9cis lostxe2x80x9d from between and/or measurement of web tension detects that the web tension xe2x80x9cis lostxe2x80x9d. In the method and the device in accordance with the present invention, the free final end or tail of the cut-off web is wound around a paper guide roll placed ahead of the cutter blade, in which case the web does not remain, for example, in airborne web dryers, for example, in connection with cutting off, and therefore it is easier to clean the coating machine. The web wound around the roll can also be unwound from the roll directly, for example, onto the broke conveyor or into the pulper, and a web break can be cleared up with very quick cleaning. Owing to the realization in accordance with the present invention, for example, in a paper mill, economies of millions of Finnish Markkas are obtained in a year in terms of shorter web break times or in the form that the invention permits running of the coating machine with an operating team of fewer persons than in the prior art.
A very little amount of broke to be cleared is achieved in off-machine coating machines if the web is wound around a pick-up roll placed before the web break point and if the machine portion that precedes the roll is slowed down in a controlled way so that the web remains whole. In such a case, the web also remains whole in the unwind stand, which reduces the amount of broke that is formed significantly. After the break, the web can be wound back to the unwind stand, or it can be unwound in a controlled way, for example, into the basement.
As the pick-up roll, it is advantageously possible to use the roll solutions described in the same applicant""s Finnish Patent Application No. 974417 (filed Dec. 4, 1997).
In a preferred embodiment of the invention, the pick-up roll is a suction roll, into which an intensive vacuum is passed substantially at the time of web cut-off.
In a second preferred embodiment of the invention, a constant slight vacuum is maintained in the suction roll to stabilize the running of the web, and substantially at the time of web cut-off an intensive vacuum is passed into the suction roll.
In a third preferred embodiment of the invention, a vacuum that has been set invariable is maintained in the suction roll, which vacuum is sufficient to suck the cut-off web to around the suction roll at the time of web cut-off, but which vacuum does, however, not cut off the web or have an interfering effect on the run of the web during normal running.
According to a fourth preferred embodiment of the invention, a moistening jet that increases the adhesion is applied onto the pick-up roll. Such a moistening jet affixes the cut-off web reliably onto the pick-up roll.
According to a fifth preferred embodiment of the invention, the cut-off web is guided, by means of an air foil box fitted in connection with the pick-up roll and by means of blowings of air fitted in said box, so that it is wound onto the pick-up roll placed before the cutter blade. In the vicinity of the face of the pick-up roll, air jets parallel to the sense of rotation of the pick-up roll as well as a carrier face have been fitted, which carrier face extends a distance around the pick-up roll. By means of the air jet placed nearest to the cutter blade, the cut-off web is guided by means of a coanda effect into the space formed by the air foil box and the pick-up roll and further to around the pick-up roll.